Glycidoxypropyl silanol and polydimethyl siloxanes as mold release agents

ABSTRACT

An aqueous solution of suspension of glycidoxypropyl silanol and polydimethyl siloxanes having a number average molecular wieght of more than 100,000 and their use as mold release agents with good release values over a relatively large number of molding cycles in the molding of rubber and plastics.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to aqueous solutions or suspensions containingglycidoxypropyl silanol and polydimethyl siloxanes having a numberaverage molecular weight or more than 100,000 as mold release agents forplastics.

2. Statement of Related Art

Various mold release agents containing the following substances areknown and are commercially available:

1. water-soluble surfactants;

2. silicone oils containing organic solvents;

3. crosslinkable silicone resins containing organic solvents, and

4. silicone latices.

In addition to certain advantages however, the mold release agentsdisclosed above also show serious disadvantages. Thus, although theyshow ready biodegradability and produce a good release effect, the moldrelease agents of group 1 are stripped from the mold during each releasecycle. To produce a thin film on the mold, the mold release agents ofgroup 2 have to be dissolved in organic solvents. Since these solventsare inflammable and since the mold release agents are applied to moldsheated to around 160° C., they can only be used in explosion-proofplants. If, on the other hand, non-inflammable halogenated hydrocarbonsare used as the solvents, the usual disposal measures have to be takendue to the solvent vapors formed. The mold release agents of group 2also have to be re-applied after each cycle. In addition, they remainbehind on the surfaces of the molding which therefore have to be cleanedbefore lacquering.

The mold release agents of group 3 have the disadvantages alreadymentioned due to the presence of solvents in them, although they doremain in place for several molding cycles. Although the mold releaseagents of group 4 are free from organic solvents, they are also easilystripped so that they often have to be re-applied and, in addition,cause soiling of the mold in practice. Accordingly, there is a need formold release agents which are free from organic solvents and which donot have to be replaced for at least several molding cycles.

DESCRIPTION OF THE INVENTION

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients or reaction conditions usedherein are to be understood as modified in all instances by the term"about".

It has now been found that aqueous emulsions, solutions, or suspensionscontaining glycidoxypropyl silanol and polydimethyl siloxanes having anumber average molecular weight of more than 100,000, which are freefrom organic solvents, do not have to be replaced until after ten ormore molding cycles. Apart from traces of alcohol formed duringhydrolysis, the solutions or suspensions to be used in accordance withthe invention contain only water as solvent, form a stripping-resistant,effectively releasing film in the mold, which withstands a number ofvulcanization cycles, and does not adhere to the surface of themoldings, so that there is no need for cleaning before lacquering orbonding. The molds treated with the mold release compositions of theinvention are preferably molds for rubber or plastics.

The present invention also relates to a mold release agent containing0.5 to 3% by weight glycidoxypropyl silanol and 0.2 to 2% by weight of asilicone latex, the silicone latex containing approximately 25 to 55% byweight of a polydimethyl siloxane having a number average molecularweight of more than 100,000 in aqueous emulsion, in aqueous solution, orin suspension.

The glycidoxypropyl silanol used in accordance with the invention is aknown compound which can be obtained by hydrolysis of commercial3-glycidoxypropyl trimethoxy or triethoxy silane with dilute acids,preferably acetic acid, at pH values of 4 to 4.5. In addition to theglycidoxypropyl silanol, the hydrolysis product may contain otherhydrolysis products (through ring opening of the epoxide group) andcondensates (through reactions at the silanol group). Silicone laticesfor use in accordance with the invention are commercially availablecompounds.

The invention is illustrated but not limited by the following Examplesand Comparison Examples.

EXAMPLES EXAMPLE 1 (a) Preparation of Glycidoxypropyl Silanol:

In a three-necked flask equipped with a stirrer, dropping funnel andreflux condenser, 500 g water were adjusted with dilute acetic acid to apH value of 4 to 4.5. 15 g glycidoxypropyl triethoxysilane were thenadded dropwise, the mixture being heated to 90° C. This temperature wasmaintained for 1 hour.

(b) Preparation of the Release Agent

The cooled silanol solution obtained in step a) was mixed while stirringwith 6,5 g of a polydimethyl siloxane latex having the followingproperties: anionically stabilized emulsion, number average molecularweight of the polydimethyl siloxane above 100,000, content ofnon-volatile constituents 40% by weight, specific gravity 1.02, pH value11.2, viscosity 1000 cps. The product is commercially available.

EXAMPLE 2

A mold release agent containing 3% by weight glycidoxypropyl silanol and1% by weight silicone latex was prepared in the same way as described inExample 1.

EXAMPLE 3

A mold release agent containing 1.3% by weight glycidoxypropyl silanoland 0.22% by weight silicone latex was prepared in the same way asdescribed in Example 1.

The test mold used was a construction comprising an upper circular plate85 mm in diameter provided with 16 M12 hexagonal screws, a lowercircular plate formed with grooves into which the rubber was pressed anda rubber blank arranged between the two circular plates. A rubbermixture having the following composition was used:

    ______________________________________                                        SBR                100    parts by weight                                     Stearic acid       1      part by weight                                      ZnO                10     parts by weight                                     Antiager           1      part by weight                                      Paraffin (42-44° C.)                                                                      1      part by weight                                      HAF carbon black   70     parts by weight                                     Accelerator        1      part by weight                                      Sulfur             0.8    part by weight                                      ______________________________________                                    

The vulcanization conditions were as follows:

    ______________________________________                                        Vulcanization temperature:                                                                           170° C.                                         Vulcanization time:     7 minutes                                             Pressure:              150 bar                                                ______________________________________                                    

To carry out the release tests, the release agent was sprayed onto themold described above and baked for 30 minutes at 150° C. The rubberblank was then molded.

The upper and lower circular plates were vertically released in atensile testing machine. The maximum release values were recorded.Further molding and release cycles were then carried out with nore-application of release agents.

The results obtained with the release agents according to Examples 1 to3 are shown in the Table at the end of the Examples.

In addition, comparison tests I to VIII were carried out under theconditions described above, the following compositions being tested:

I : without release agent

II : solvent-containing silicone resin (commercially available)

III : 1% surfactant (alkane sulfonate) in water (commercially available)

IV : 1% of the silicone latex used in Example 1

V : 3% of the glycidoxypropyl silanol used in Example 1

VI : 3% hydrolyzed aminoethyl aminopropyl triethoxysilane (commerciallyavailable)

VII : 5% Y-aminopropyl triethoxysilane

VIII : 3% hydrolyzed vinyl triethoxysilane

Mixtures of the silicone latex of Example 1 with the hydrolyzed silanesof Comparison Examples VI, VII and VIII were not stable and,accordingly, did not produce useful mold release agents.

The results of the comparison tests are also shown in the Table at theend of the Examples.

It can be seen from the Table that the mold release agents of Examples 1to 3 according to the invention produce an excellent release effect,even in the 1Oth molding cycle. Compared with the individual components(comparison tests IV and V), highly enhanced effects were obtained withthe combinations according to the invention. Finally, the release agentsaccording to the invention have the advantage over Comparison Example IIin that they contain no solvents.

                  TABLE                                                           ______________________________________                                        (Release values in N)                                                                1st release                                                                           2nd release                                                                             5th release                                                                             10th release                                      value   value     value     value                                      ______________________________________                                        Example                                                                       1        7         6         7       7                                        2        12        15        17      20                                       3        7         7         8       8                                        Comparison                                                                    Example                                                                       I        45        45        45      45                                       II       9         9         8.5     9                                        III      8         12        20      40                                       IV       8         11        15      25                                       V        40        35        17      15                                       VI       16        20        35      45                                       VII      45        45        45      45                                       VIII     45        45        45      45                                       ______________________________________                                    

We claim:
 1. A mold release composition substantially free from organicsolvents in the form of an aqueous emulsion, solution, or suspensioncomprisingA. from about 0.5 to about 3% by weight of glycidoxypropylsilanol, and B from about 0.2 to about 2% by weight of an aqueoussilicone latex containing from about 25 to about 55% by weight of apolydimethyl siloxane having a number average molecular weight of morethan 100,000.
 2. A method of coating a mold with a mold release agentcomprising applying to the mold the mold release composition of claim 1and carrying out at least ten molding cycles before reapplying said moldrelease composition to the mold.
 3. The method of claim 2 wherein themold is a mold for rubber or plastics.